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Hi,

The SRS light is on when the car (1992 500SL) is driven. The dealer has checked the diagnostics and says it is because of a drivers seatbelt buckle failure and this needs to be replaced - surprise surprise - for $380. Can I use one from a different model car? There are no W129s at the wreckers so I'm thinking I could substitute one from another model? Alternatively, can I get the buckle fixed by an autoelectrician? Any help is gratefully received, especially by my wallet.

Cheers
 

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2003 SL500, 2003 SL55, 2005 S55, (2) 1991 300SLs, 1994 E320 cabriolet
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I don't think you can substitute a buckle from another model. Your car has a cable which runs from the buckle to the inertia reel of the seatbelt -- a feature I believe is unique to the SL.

But you may be able to fix your existing buckle. Your problem is probably the switch inside. It may simply need to have its contacts cleaned. It is possible to partially disassemble the buckle and get to the switch -- I've done it before -- but I'm afraid I can't offer any instruction because it was too long ago.
 

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97 SL500
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1,259 Posts
u may be able to cut the wires and short them out, or

maybe just cutting the wires, hece fooling the computer. Caution: this determination can only be made with a good set of electrical schematics. i'll search around for schematics. i would try to get to the switch and clean it out along with all the electrical connectors you come across.
 

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2003 SL500, 2003 SL55, 2005 S55, (2) 1991 300SLs, 1994 E320 cabriolet
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RE: u may be able to cut the wires and short them out, or

Cutting the wires will not work, since the controller can sense an open-circuit fault as well as a short-circuit fault. But Carlos is on the right track, for what would surely work would be to unplug the switch at the connector under the seat and wire a 100-ohm resistor across the terminals. At all times this would make the controller think the belt is buckled.
 

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Hi, I had the same problem, let me tell you how it got solved.The tech at mercedes told me to check that the back rest of the seats are fully locked in. I put sheep skins on and the passenger seat had not clicked in. I moved the seat forward and bingo the back rest poped in and the light went off. Try this and let me know.regards Hilton
 

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1999 SL 500 Sport Pk
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29 Posts
My SRS light stays on as well so if you figure this out please post...
Thanks,
Mike
 

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2009 SL550 Silver Arrow Launch Edition, 2013 Mercedes Benz C300 4Matic
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986 Posts
I too have a "Lazy" SRS light due to a seatbelt buckle on the passenger side. I'm not worried about it as the system is operational after the first 5 minutes or so, but it is annoying. Curious also about solutions. Cost of repair: $300.00+
 

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1995 500SL
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141 Posts
I too have a bad seatbelt switch on the driver's side causing the SRS to stay lit. I know the system is good so I just ignore the light for the few minutes it remains lit. I assume there is a similar switch on the passenger side sooo.. ILO replacing the switch for $300 plus, can the switch connectors be swapped (I cruse around mostly by myself anyway)? Also - Has anyone tried spraying the inside of the switch with a solvent to clean contacts?
 

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1995 SL500
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169 Posts
SRS Warning Light

I saw a post earlier concerning the SRS light and the code signifying that the pass seat belt latch needs to be replaced. Thanks to whoever posted the following repair. I bought a can of spray Contact Cleaner @ Radio Shack. I sprayed the innards of the buckle and then blew it out with a air pressure and also vacuumed it. I did it several weeks later since I still had some spray left over and I caught the booger. Wal-la. Now works like it is supposed to. Savings $580. Thank you Forum.:bowdown::bowdown::bowdown::thumbsup:
 

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1995 SL 320
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76 Posts
I’ve sprayed cleaner and used air but this has not fixed my problem. Has anyone found a solution to buckle switch?

My mechanic a couple years back wrote on invoice that I had SRS code 24 (driver seatbelt buckle switch) and code 25 (passenger seatbelt buckle switch) appeared.

Looking for a solution. :)
 

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1995 SL 320
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76 Posts
Any way to test seatbelt buckle on R129

Is there a way to test the seatbelt buckle to see SRS code is coming from the buckle? There are a couple connections that connect the buckle. Any suggestions?

Can I bypass the SRS at these connections so the SRS codes will go away?
 

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Outstanding Contributor
2003 SL500, 2003 SL55, 2005 S55, (2) 1991 300SLs, 1994 E320 cabriolet
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Is there a way to test the seatbelt buckle to see SRS code is coming from the buckle?
Refer to the diagnostic manual. Moderator MAVA can provide the schematic from the Electrical Troubleshooting Manual. Perhaps you should send him a PM.
 

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1995 SL 500
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64 Posts
Been there done that.. Get a replacement from Ebay ..take the seat apart, lower and back, and replace the buckle or check the connection loop within the buckle, buckle meaning the stationary part at the seat. There is a contact sensor in there around a loop which sends a signal to the controller under the seat when the moving part connects to it.

The SRS light has to be reset via a STAR unit or at the dealer. There are no pins to reset it in the on board connector in the engine bay.

With my issue, I reset the light but the buckle would not operate properly until I replaced it. I couldn't really justify having a passenger with a faulty seatbelt in the car.

The seat doesn't have to be removed but does need to be free to move up high enough to replace the buckle connector. Ive been through the entire system which is very well designed but has it's difficulties when trying to replace parts. These seats are very heavy so a block of wood helps to keep it high enough to remove the buckle connector. Just take photo's of the routing so you get it right the first time.

Cheers,
 

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1995 SL 320
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Been there done that.. Get a replacement from Ebay ..take the seat apart, lower and back, and replace the buckle or check the connection loop within the buckle, buckle meaning the stationary part at the seat. There is a contact sensor in there around a loop which sends a signal to the controller under the seat when the moving part connects to it.

The SRS light has to be reset via a STAR unit or at the dealer. There are no pins to reset it in the on board connector in the engine bay.

With my issue, I reset the light but the buckle would not operate properly until I replaced it. I couldn't really justify having a passenger with a faulty seatbelt in the car.

The seat doesn't have to be removed but does need to be free to move up high enough to replace the buckle connector. Ive been through the entire system which is very well designed but has it's difficulties when trying to replace parts. These seats are very heavy so a block of wood helps to keep it high enough to remove the buckle connector. Just take photo's of the routing so you get it right the first time.

Cheers,
Thanks for the information.

My seatbuckle works all the time. The light just stays on for a few minutes then turns off.

Is there a way to test the seatbelt buckle (connection loop) without taking the buckle apart? Test with a multimeter at wire connections to control box under the seat?
 

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1988 560SL
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49 Posts
I am having trouble with understanding the wiring harness under the drivers seat? I replaced the seat with new pad after removing the seat reconnected everything but the red connector two wire which I can’t determi where this is to plug into. I hinestodomt remember this connector when I took the seat out. After plugging in in the larger two wire black connector which I believed was the only connection I now get a srs warning light on start up. Does anyone know if the red connector is supposed to connect and if so where does this connect to? I don’t recall any other wiring harness under the seat while replacing the horse hair pad
 

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I am having trouble with understanding the wiring harness under the drivers seat? I replaced the seat with new pad after removing the seat reconnected everything but the red connector two wire which I can’t determi where this is to plug into. I hinestodomt remember this connector when I took the seat out. After plugging in in the larger two wire black connector which I believed was the only connection I now get a srs warning light on start up. Does anyone know if the red connector is supposed to connect and if so where does this connect to? I don’t recall any other wiring harness under the seat while replacing the horse hair pad
Yes. I have the same issue after removing the seat and installed it back (2012 ML350). Still waiting for the answer with thanks.
 

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2002 SL500 Silver Arrow
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830 Posts
not sure if this is what you are asking - but once the SRS light sets, you need to clear it with star diagnostic. I changed my seat belt buckle and started the car with the airbag disconnected while waiting for the part. Had to go through the 38-pin port under the hood (my car is a 2002) and cleared it in a few keystrokes. It will not clear itself just because there is a good part/connection there now.
 
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